1. Field of the Invention
The present invention relates to a flushing processing unit and method of a switching device in a network using Spanning Tree Protocol (STP), and more particularly, to a flushing processing unit and method of a switching device in a network using Spanning Tree Protocol (STP) for preventing flushing at unnecessary ports and unnecessary switches upon topology change and reducing a switch process load and a network load caused by flooding.
2. Description of the Related Art
In a normal network configuration state, address information of a registered host is stored in a filtering database. Address information changes only when a physical position of a host changes.
Upon a change in topology, however, each switch equipment processing switch functions, Spanning Tree Protocol (STP) flushes and registers the stored address information on the basis of a new topology.
Contemporary methods for reducing unnecessary flushing were proposed, but unnecessary flushing still remains.
Institute of Electrical and Electronics Engineers (IEEE) 802.1D Spanning Tree Protocol (STP) was developed to recover from a failure between bridges or switches providing layer-2 switching or prevent undesirable loops in a network. That is, Spanning Tree Protocol (STP) is a technology for securing network stability by detecting and removing undesirable loops that cause the indefinite transmission of packets through two or more network paths in configuring a network, and upon the occurrence of a failure, configuring a new topology to recover from the failure.
IEEE 802.1w Rapid Spanning Tree Protocol (RSTP) was developed to provide a solution to a problem of Spanning Tree Protocol (STP) in which reconfiguration is slow in the event of topology change.
IEEE 802.1s Multiple Spanning Tree Protocol (MSTP) is a way to group Virtual Local Area Networks (VLANs) and balance network load in Virtual Local Area Networks (VLAN)-aware switch. IEEE 802.1s Multiple Spanning Tree Protocol (MSTP) was developed to configure several instances on the basis of Rapid Spanning Tree Protocol (RSTP) and operate Rapid Spanning Tree Protocol (RSTP) by one per instance.
In cases where a specific link on a network fails and where a bridge priority or port priority changes, a change in a path actually transmitting data packets occurs, changing an active topology.
In the event of generation of an active topology, a host address stored in a filtering database should be re-registered with new information.
For this, information of the filtering database is flushed such that new information is registered.
In cases where the filtering database is flushed, flooding takes place because the host address (a Media Access Control (MAC) address in Ethernet) for forwarding packet over the network has not been registered.
Flooding increases a load in the whole network. Thus, it is desirable to avoid flooding in Spanning Tree Protocol (STP) as possible.
If a change in topology takes place, a corresponding bridge sends a Topology Change Notification (TCN) message (in Rapid Spanning Tree Protocol (RSTP), Bridge Protocol Data Unit (BPDU) is set with a Topology Change (TC) bit) to notify the event.
Upon receiving the Topology Change Notification (TCN) message, a bridge deletes host addresses registered through all other ports excepting a port receiving the Topology Change Notification (TCN) message, from the filtering database.
In order to avoid flooding if possible during the evolution from Spanning Tree Protocol (STP), Rapid Spanning Tree Protocol (RSTP) to Multiple Spanning Tree Protocol (MSTP), proposed were methods for efficiently detecting a topology change to reconfigure an active topology and methods for efficiently flushing a filtering database as follows.
Unlike IEEE 802.1D defining unconditionally that a change in a port state between blocking and forwarding is a change in topology, Rapid Spanning Tree Protocol (RSTP) defines that a change in a port state from blocking to forwarding is a change in topology.
In Rapid Spanning Tree Protocol (RSTP), a change in an edge port state does not lead to a change in topology.
For this, AutoEdge State Machine capable of detecting an edge port automatically was proposed.
In Rapid Spanning Tree Protocol (RSTP), an optional statement is a function of registering host addresses, which have been registered to a root port, to an alternate port in cases where the root port fails and the alternate port changes into the root port.
In Multiple Spanning Tree Protocol (MSTP), a Bridge Protocol Data Unit (BPDU) includes an independent Topology Change Notification (TCN) message for each instance.
Thus, proposed was an efficient method in which, upon receiving a corresponding Topology Change Notification (TCN) message for a corresponding instance, flushing is performed only for a port belonging to the instance with no flushing for a whole port excepting a reception port.
In a contemporary sequence of events occurring when one link fails in an Spanning Tree Protocol (STP) network including one or more switching devices, flushing happens unnecessarily in all switches connecting on topology instead of only happening to related ports, therefore, a network load is unnecessarily increased.
Additionally, deleting and/or registering a host address is again performed, which causes a deterioration of the process performance of the switch.
New packets are forwarded via a new active topology and are re-registered to the filtering database, so normal data transmission is again performed; however, there is a drawback that while forwarding and re-registering, flooding for a corresponding host address takes place, thus causing an increase of the entirety of the network load.